Fibrous composite material and process for producing the same

ABSTRACT

A fiber-composite material ( 7 ) is comprised of a yarn aggregate ( 6 ) in which yam ( 2 A,  2 B) including at least a bundle ( 3 ) of carbon fiber and a carbon component other than carbon fiber is three-dimensionally combined and integrally formed without separation from each other; and a matrix made of Si—SiC-based materials ( 4 A,  4 B,  5 A,  5 B) filled between the yarn ( 2 A,  2 B) adjacent to each other within the yarn aggregate ( 6 ). A method of preparing fiber-composite material is comprised of the steps of: producing bundles ( 3 ) of carbon fiber by impregnating a component of powdery carbon into the bundles ( 3 ) of carbon fiber, which eventually forms a matrix shape; forming a plastic coat around the bundles ( 3 ) of carbon fiber to obtain an intermediate material; molding the intermediate material to obtain a molded product by making the intermediate material into a yarn-shape and laminating a predetermined amount of the material, or burning the molded product to obtain a burned product; holding the molded product or the burned product and Si, at 1100 to 1400° C. in an atmosphere of inert gas; and heating the molded product or the burned product and Si to a temperature from 1450 to 2500° C., to thereby impregnate Si—SiC-based material into the inside of pores of the molded product or the burned product. A light and strong composite material is provided, which has excellent shock resistance, corrosion resistance in a strong oxidation and corrosion environments, creep resistance, spalling resistance, wear resistance, a low friction coefficient and a self-restorative ability by which a defect is healed.

TECHNICAL FIELD

The present invention relates to a fiber-composite material that can beused as an ultra-high-heat-resistant structural material, and a highlylubricated and wear resistant material, and more particularly to amethod of preparing the fiber-composite material.

BACKGROUND OF THE INVENTION

The development of space-round-trip aircraft and space planes in thespace development field, high-temperature burning gas turbines in theenergy field, and high-temperature gas furnaces and fusion reactors inthe atomic energy field have experienced rapid development recently.

As an energy source next to nuclear energy and solar energy, applicationof hydrogen energy has been researched. In this process, expensivemetals and fine ceramics have been examined as vessels for thereactions. High strength and high reliability (toughness, shockresistance) materials at medium or high temperatures (200 to 2000° C.),and durability that is not affected by the environment (corrosionresistance, oxidation resistance, radiation resistance) are demanded onthese structural elements.

Today, as to ceramic materials having excellent heat resistance, siliconnitride and silicon carbide materials are being developed as newceramics. However, these materials have a defect of brittleness as theirintrinsic property, and they are extremely fragile if cracked and arealso susceptible to thermal and mechanical shock.

As means for overcoming these defects inherent in ceramics, aceramics-based composite material (CMC) that is combined with continuousceramics-based fiber has been developed. Because the material has highstrength and high toughness even at high temperature, and has excellentshock resistance and excellent durability against various environments,the research and development on the material is actively being done asthe main ultra-high heat-resistant structural material chiefly in Europeand the USA.

For example, several hundred to several thousand pieces of long ceramicfibers having a diameter of about 10 μm are bundled to form fiberbundles (yarn), and the fiber bundles are arranged two or threedimensionally to form one-direction sheets (UJD sheet) or various kindsof cloths. These sheets or cloths are laminated to make a preformedproduct with a predetermined shape (fiber preform). To make a matrixwithin the preformed product by the CVI method (Chemical VaporInfiltration: Chemical-vapor impregnating method) or by the inorganic-polymer-impregnation burning method, ceramic powder is filled into theabove-mentioned preformed product by casting-molding method and then issintered to make a matrix. Thus, ceramics-based fiber-composite material(CMC) that is combined with fibers in a ceramic matrix has beendeveloped.

As specific examples of CMC, C/C composite and SiC fiber-reinforcedSi—SiC composite are known. The former is produced by forming a matrixmade of carbon in the gap among carbon fibers arranged in two-orthree-dimensional directions, and the latter is produced by impregnatingSi into the molded product comprising SiC fibers and SiC particles.

In British Patent Specification No. 1457757, the processing method ofimpregnating C/C composite with melting Si is disclosed. According tothe method, the composite material that is a C/C composite impregnatedwith Si is supposed to be produced.

C/C composite has been employed in a wide scope of fields because of itsexcellent shock resistance owing to its high toughness, of its lightnessand its excellent strength, but the composite has a limitation in beingused as ultra-high heat-resistant structural material, because thecomposite cannot be used at high temperature in the presence of oxygensince the composite is composed of carbon. Further, the composite has adefect of low abrasion resistance when used as sliding elements becauseof its rather low hardness and low compression strength.

On the other hand, SiC fiber-reinforced Si—SiC composite is excellent inoxidation resistance, creep resistance and in spalling resistance, butthe composite is easily scratched. Also, the SiC fiber has a problemthat the fiber cannot be used as such structural material as a turbineblade that has a complex shape or a thin section, because of the lowshock resistance of the fiber. The Sic fiber is inferior in lubricatingproperty compared to Si—SiC or the like, and the drawing effect betweenthe body material and fiber is small, which leads to the inferiortoughness compared to C/C composite.

In the composite material described in the British Patent SpecificationNo. 1457757, which is a C/C composite impregnated with Si, the commonC/C composite that has been known is used, and the composite materialhas the structure that has a lot of fine pores in the whole body. Thatis, as described in Example 1 of the British Patent Specification No.1457757, after carbon fiber is coated with phenol resin, the fiber isarranged in a mold, compressed and cured so that the desired fiberdirection and shape are obtained, and then the obtained molded productis released from the mold and is heated at 800 to 900° C. in nitrogenatmosphere to carbonize the phenol resin. Thus, C/C composite, havingthe structure in which the fiber is orientated in one direction and inwhich the fiber is laminated, is obtained.

In such C/C composite, the phenol resin is carbonized to become a partof the carbon matrix, but because the rate of carbonization is about50%, the C/C composite has a structure having a lot of fine pores in thewhole body. When this C/C composite is dipped in melting Si toimpregnate Si, although the vicinity of the surface thereof is permeatedwith Si, it is impossible to make Si permeate into the whole C/Ccomposite, especially into the center part homogeneously. Therefore, theC/C composite has still the defect that is characteristic of the C/Ccomposite material and that has not yet been solved.

In addition, when the C/C composite having such structure is impregnatedwith Si, the structure of carbon fiber near the surface is brokenbecause of being directly contacted with high temperature melted Si. Asa result, there arises a problem that the C/C composite loses its shockresistance, strength, high lubricant property and wear resistance.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-mentionedproblem, and an object of the present invention is to provide acomposite material having excellent shock resistance, corrosionresistance in strong oxidation and corrosion environments, creepresistance, spalling resistance, wear resistance, low frictioncoefficient, further, lightness and strength. Additionally, the presentinvention has a self-restorative ability by which a defect is healedunder a certain condition.

The present invention provides a fiber-composite material comprising: ayarn aggregate in which yarn including at least a bundle of carbon fiberand a carbon component other than carbon fiber is three-dimensionallycombined and integrally formed without separation from each other; and amatrix made of Si—SiC-based material filled between the yarn adjacent toeach other within the yarn aggregate.

In the present invention, preferably, the matrix has a silicon carbidephase having grown along the surface of the yarn, the matrix has thesilicon phase comprising silicon, and more preferably, the siliconcarbide phase has grown between the silicon phase and the yarn.

The matrix may have an inclined composition in which the content rate ofsilicon becomes higher at increasing distances from the surface of theyarn. Preferably, the yarn aggregate includes a plurality of yarn arrayelements, each of the yarn elements is formed by arranging the pluralityof yarns in a substantially parallel direction and two dimensionally,and each of the yarn array elements is laminated to form the yarnaggregate. Then, preferably, the yarn array elements adjacent to eachother are structured such that the longitudinal direction of each yarnintersects with each other.

In the present invention, the matrices are connected to each otherwithin the fiber-composite material to form a three-dimensional networkstructure. More specifically, the matrices are arranged in asubstantially parallel direction and two-dimensionally within each ofthe yarn array elements, and the matrices having grown within each ofthe yarn array elements adjacent to each other are connected to eachother, to thereby form a three-dimensional lattice of the matrices.

According to the present invention, there is provided a method ofpreparing fiber-composite material, comprising the steps of: producingbundles of carbon fiber by impregnating a component of powdery carbonand a component of organic binder into the bundles of carbon fiber,which eventually forms a matrix shape; forming a plastic coat around thebundles of carbon fiber to obtain an intermediate material; molding theintermediate material to obtain a molded product by making theintermediate material into a yarn-shape; then, forming the intermediatematerial into a sheet if circumstances require; and laminating apredetermined amount of the material, or burning the molded product toobtain a burned product; holding the molded product or the burnedproduct and Si, at 1100 to 1400° C. in an atmosphere of inert gas; andheating the molded product or the burned product and Si to a temperaturefrom 1450 to 2500° C., to thereby impregnate Si—SiC-based material intothe inside of pores of the molded product or the burned product.

In the method, preferably, the molded product or the burned product andSi are held at a temperature of from 1100 to 1400° C. under a pressureof 0.1 to 10 hPa for one or more hours, and an inert gas is controlledto flow in an amount of 0.1 or more normal litters (NL) per 1 kg of thetotal weight of the molded product or the burned product and Si.Preferably, the molded product or the burned product and Si are heatedto a temperature of from 1450 to 2500° C. under a pressure of 0.1 to 10

BRIEF DESCRIPTION OF THE DRAWINGS

The file of this patent contains at least one drawing executed in color.Copies of this patent with color drawing(s) will be provided by thePatent and Trademark Office upon request and payment of the necessaryfee.

FIG. 1 is a perspective view schematically showing the configuration ofyarn aggregate of a fiber-composite material according to the presentinvention.

FIGS. 2(a)-2(b) are cross-sectional views schematically showing themicrostructure of the main part of a fiber-composite material accordingto the present invention, in which FIG. 2(a) is a cross-sectional viewtaken along the line IIa—IIa of FIG. 1, and FIG. 2(b) is across-sectional view taken along the line IIb—IIb of FIG. 1.

FIG. 3 is an enlarged view of a part of FIG. 2(a).

FIG. 4 is a partially sectional perspective view schematically showingthe microstructure of the main part of a fiber-composite materialaccording to another embodiment of the present invention.

FIG. 5(a) is a sectional view of fiber-composite material 11, and FIG.5(b) is a sectional view of fiber-composite material 16.

FIG. 6 is a color photograph of EPMA showing the structure of a ceramicmaterial viewed in a sectional direction to the surface layer of a testpiece of Example 1.

FIG. 7 is a color photograph of a reflective electronic image by SEMshowing the structure of the ceramic material in the sectional directionof the surface layer of the test piece of Example 1.

FIG. 8 is a view illustrating the microstructures shown in FIG. 6 andFIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

A fiber-composite material according to the present invention comprises:a yarn aggregate in which yarn including at least a bundle of carbonfiber and a carbon component other than carbon fiber isthree-dimensionally combined and integrally formed so as not to separatefrom each other; and a matrix made of Si—SiC-based materials filledamong the yarn adjacent to each other within the yarn aggregate.

Thus, a fiber-composite material can be given toughness by using a C/Ccomposite as the body material, which allows the fiber-compositematerial to have excellent shock resistance, lightness, high strength,high lubricant property and wear resistance. Therefore, it is possibleto overcome the defect of low shock resistance which SiCfiber-reinforced Si—SiC composites have and to use the composites as thestructural material that has a complex shape or a thin section. Sincethe C/C composite is produced in such a way that the C/C composite hascontinuous pores inside thereof, the Si—SiC based material, impregnatedinto the pores, has a continuous structure and a three-dimensionalnetwork structure. Therefore, any cut portion has higher wear resistancecompared with the C/C composite that is the body material, and maintainsthe lubricant property the C/C composite has intrinsically.

By arranging the layer comprising Si—SiC-based material on the surface,it becomes possible to give oxidation resistance, creep resistance andspalling resistance to the fiber-composite material, to improve the lowoxidation resistance a C/C composite has, and to use the fiber-compositematerial at high temperature even in the presence of oxygen. Thus, thefiber-composite material can be used as an ultra-high heat resistancestructural material.

Hereinbelow, the novel fiber-composite material according to the presentinvention will be described.

The material is a material of new idea, which is made by givingimprovement to the basic composition based on a so-called C/C composite.

The C/C composite produced in the following process is known. Severalhundred to several ten thousand pieces, ordinarily, of carbon fiberhaving a diameter of about 10 μm are bundled to obtain fiber bundles(yarn), and the fiber bundles are arranged two-dimensionally to form aone-direction sheet (UD sheet) or various kinds of cloth. These sheetsor cloths are laminated to form a preformed product with a predeterminedshape (fiber preform). A matrix made of carbon is formed within thepreformed product by the CVI method (Chemical Vapor Infiltration:Chemical-vapor impregnating method) or by theinorganic-polymer-impregnation sintering method to obtain a C/Ccomposite.

The fiber-composite material has an excellent characteristic ofmaintaining the structure of carbon fiber without damaging thestructure, which results from the fiber-composite material beingproduced by the specific method to be described below using a C/Ccomposite as a body material . As described in the above-mentionedBritish Patent Specification No. 1457757, the fiber-composite materialthat is a C/C composite impregnated with Si is known. However, becausethe structure of carbon fiber is broken in the material, the propertiesof C/C composite such as shock resistance, strength, high lubricantproperty and wear resistance is lost.

The fiber-composite material according to the present invention isapplied with the specific treatment in which a soft coat made fromplastic such as thermoplastic resin is formed at least around the carbonfiber bundle to obtain a soft intermediate material, and the material ismade to be yarn-shaped. Then the material is formed into a sheet ifcircumstances require, and the sheet is laminated and subjected to hotmolding. High temperature, molten Si causes a contact reaction firstwith carbon particles except for the carbon fiber, or highly activatedcarbon generated by thermal decomposition of an organic binder and/orthe plastic coat, and is not directly contacted with the carbon fiberbundles. Thus, the structure of the carbon fibers is not damaged.

Moreover, the fiber-composite material according to the presentinvention has the microstructure filled with the matrix made ofSi—SiC-based material among the yarns that are adjacent to each other inthe yarn aggregate.

In the present invention, Si—SiC-based material is a general term forthe material that contains Si and silicon carbide as the main component.In the present invention, when Si is impregnated into the C/C compositeor into the molded product made of the C/C composite, Si reacts mainlywith the component of carbon, except for carbon fibers, or remainedcarbon in the composite, and is partially carbonized to grow Si a partof which is carbonized among the yarn aggregates. The matrix may containsome intermediate phases from the silicon phase in which silicon hasalmost purely remained to the almost-pure silicon carbide phase. Thatis, the matrix is typically composed of the silicon phase and thesilicon carbide phase, but the matrix may contain the Si—SiC coexistingphase in which the carbon content changes with gradient based on siliconbetween the silicon phase and the silicon carbide phase. Si—SiC-basedmaterial is a general term for the material in which the carbonconcentration changes from 0 mole % to 50 mole % in such Si—SiC system.

In the fiber-composite material, preferably, the matrix comprises thesilicon carbide phase that has grown along the surface of the yarn. Inthis case, the strength of each yarn itself is further improved, and thefiber-composite material is hardly damaged.

In the fiber-composite material, preferably, the matrix comprises thesilicon phase that is made of silicon, and the silicon carbide phase hasgrown between this silicon phase and the yarn. In this case, the surfaceof the yarn is strengthened by the silicon carbide phase. At the sametime, the micro-dispersion of stress is further promoted because thecentral part of the matrix is composed of the silicon phase that has arelatively low hardness.

In the fiber-composite material, preferably, the matrix has an inclinedcomposition in which the content rate of silicon becomes higheraccording to the distance from the surface of the yarn.

In the fiber-composite material, preferably, the yarn aggregatecomprises more than one yarn array element, each of the yarn arrayelements being formed by arranging more than one yarn two-dimensionallyin a nearly parallel direction, and each of the yarn array elementsbeing laminated. The fiber-composite material, therewith, has alaminated structure in which the yarn array elements that have aplurality of layers are laminated toward one direction.

In this case, more preferably, the direction of the length of each yarn,in the yarn array elements adjacent to each other, intersects eachother. The dispersion of stress is further promoted therewith. Morepreferably, the direction of the length of each yarn, in the yarn arrayelements adjacent to each other, intersects each other at right angles.

Preferably, the matrices form a three-dimensional network structure bybeing connected with each other in the fiber-composite material. In thiscase, more preferably, the matrices are arranged, in each of the yarnarray elements, two-dimensionally in a nearly parallel direction, thematrices have grown, in each of the yarn array elements adjacent to eachother, being connected with each other, and the matrices forms athree-dimensional lattice structure therewith.

The gap among the yarns adjacent to each other, may be filled with thematrix to the level of 100%, but the gap among the yarn may be partiallyfilled with the matrix.

The component of carbon other than carbon fiber in the yarn is,preferably, carbon powder, and, more preferably, the carbon powder thatis made to be graphite.

FIG. 1 is a perspective view schematically showing the idea of yarnaggregate. FIG. 2(a) is a cross-sectional view taken along the lineIIa—-IIa of FIG. 1, and FIG. 2(b) is a cross-sectional view taken online IIb—IIb of FIG. 1. FIG. 3 is an enlarged view of a part of takenfrom FIG. 2(a).

The skeleton of fiber-composite material 7 comprises the yarn aggregate6. The yarn aggregate 6 is constructed by laminating the yarn arrayelements 1A, 1B, 1C, 1D, 1E, 1F upward and downward. In each of the yarnarray elements, each yarn 3 is arranged two-dimensionally, and thedirection of the length of each yarn is nearly parallel to each other.The direction of the length of each yarn, in each of the yarn arrayelements adjacent to each other upward and downward, intersects at rightangles. That is, the direction of the length of each yarn 2A in each ofthe yarn array elements 1A, 1C, 1E is parallel to each other, and thedirection of the length thereof intersects the direction of the length,at right angles, of each yarn 2B in each of the yarn array elements 1B,1D, 1F.

Each yarn comprises fiber bundle 3 comprising carbon fiber and acomponent of carbon except carbon fiber. The yarn array elements arelaminated to form the yarn aggregate 6 that is three-dimensional andlattice shaped. Each yarn has become substantially elliptical because ofbeing crushed during the pressure molding process to be described below.

In each of the yarn array elements 1A, 1C, 1E, the gap among the yarnsadjacent to each other is filled with the matrices 8A, each of thematrices 8A runs along the surface of the yarn 2A in parallel with theyarn. In each of the yarn array elements 1B, 1D, 1F, the gap among theyarns adjacent to each other is filled with the matrices 8B, each of thematrices 8B runs along the surface of the yarn 2B in parallel with theyarn.

In this example, the matrices 8A and 8B comprise the silicon carbidephases 4A, 4B that coat the surface of the yarn and the Si—SiC-basedmaterial phases 5A, 5B in which the rate of contained carbon is lessthan in the silicon carbide phases 4A, 4B. The silicon carbide phasesmay partially contain silicon. In this example, the silicon carbidephases 4A, 4B have grown also between the yarn 2A, 2B adjacent to eachother up and down.

Each of the matrices 8A, 8B runs along the surface of the yarn in thelong and narrow shape, preferably, linearly, and each of the matrices 8Aand 8B intersects at right angles each other. The matrices 8A in theyarn array elements 1A, 1C, 1E and the matrices 8B in the yarn arrayelements 1B, 1D, 1F, which intersect the matrices 8A at right angles,are respectively connected in the gap part between the yarn 2A and 2B.As a result, the matrices 8A, 8B form a three-dimensional lattice as awhole.

FIG. 4 is a partially sectional perspective view of the main part of afiber-composite material of another embodiment of the present invention.In this example, a silicon carbide phase does not substantially existbetween the yarns 2A and 2B adjacent to each other up and down. In eachof the yarn array elements, the matrix 8A or 8B is formed individuallybetween the yarns 2A and 2A adjacent to each other, or between the yarns2B and 2B adjacent to each other. The shapes of the matrices 8A and 8Bare the same as the examples of FIG. 1 to FIG. 3 except that a siliconcarbide phase does not exist between the yarns adjacent to each other upand down. Each of the matrices 8A and 8B individually comprises thesilicon carbide phase 5C, that has grown in contact with the surfaces ofthe yarn 2A, 2B, and the Si—SiC-based material phase that has grown inthe silicon carbide phase 5C separated from the yarn.

Each of the Si—SiC-based material phase, preferably, has an inclinedcomposition in which the silicon concentration becomes lower accordingto the distance from the surface of the yarn, or preferably, comprises asilicon phase.

As shown in FIG. 5(a), the fiber-composite material 11 according to thepresent invention, preferably, comprises the C/C composite 15 and thefiber-composite material layer 13, that has grown on the surface of theC/C composite 15, is impregnated with Si, and the silicon layer 14 thathas grown on the fiber-composite material layer 13. Reference numeral 12shows the area of the body of C/C composite that has never beenimpregnated with Si. As shown in FIG. 5(b), the whole of the element 16is preferably formed with the fiber-composite material according to thepresent invention.

In the case that the fiber-composite material layer 13 is provided, thethickness thereof is preferably 0.01 to 1 mm. Further, the Siconcentration in the fiber-composite material layer preferably increaseswith increasing distance from the carbon fiber.

If the fiber-composite material according to the present inventioncontains 10 to 70% by weight of carbon fiber, the material may contain,for example, elements other than carbon such as boron nitride, boron,copper, bismuth, titanium, chromium, tungsten and molybdenum.

The thickness of the fiber-composite material layer 13, that is providedby the fact that Si—SiC is impregnated into the body material, isdescribed in more detail.

With regard to the relations between a carbon fiber bundle 3, a siliconcarbide phase 4B, and a silicon phase SB; the C/C composite 15, thelayer 13, and the silicon layer 14 correspond to the carbon fiber bundle3, the silicon carbide phase 4B, and the silicon phase 5B, respectively,in FIG. 2(a).

Here, the layer 13 has a thickness of preferably 0.01 to 1 mm, morepreferably 0.05 to 1 mm.

At this time, the layer 13 is preferably formed in such a way that theSi concentration inclines in a range of from 0/90 to 90/100 from aportion of the carbon fiber bundle 3 toward a portion of the siliconphase 5B through the silicon carbide phase 4B.

Inclination of Si concentration is hereinbelow described in detail bytaking a macroscopic view on a supposition of a block having a thicknessof 200 mm.

In the present invention, since a laminate of carbon fiber bundles isimpregnated with Si, the center of the block having a thickness of 200mm has the lower Si concentration, and a portion around the surfacelayer has the higher Si concentration. Because of this, the mostpreferable mode can be realized by forming a molded or sintered body ofa C/C composite so that the porosity becomes lower from the surfacetoward the inside and by disposing and forming a plurality of preformedsheets made of preformed yarn which has various binder pitches so thatthe binder pitch becomes higher from the inside toward the surface. Inthe case of FIG. 2(a), SiC concentration (═Si concentration) becomeslower in the order of “silicon carbide phase 4A of yarn array elements1A layer”>“silicon carbide phase 4A of yarn array elements 1Blayer”>“silicon carbide phase 4A of yarn array elements 1Clayer”>“silicon carbide phase 4A of yarn array elements 1D. Therefore,Si concentration inclines in a maximum thickness of about 100 mm in amacroscopic view. The Si concentration preferably inclines in a range offrom 90/100 to 0/100 from the surface toward the inside of the layer 13.

The fiber-composite material according to the present invention, asdescribed above, may contain one or two or more than two substancesselected from the group consisting of boron nitride, boron, copper,bismuth, titanium, chromium, tungsten and molybdenum.

Because these substances have a lubricant property, by impregnatingthese substances into the body material made of C/C composite, even inthe part of the body material impregnated with Si—SiC-based material,the lubricant property of the fiber can be maintained and the decline ofphysical properties can be prevented.

For example, the boron nitride content is preferably 0.1 to 40% byweight to 100% by weight of the body material made of C/C composite. Itis because the effect of addition of lubricant property with boronnitride cannot be adequately obtained in the concentration that is lessthan 0.1 % by weight, and, in the case in which the concentration thatis more than 40% by weight, the brittleness of boron nitride appears inthe composite material.

The fiber-composite material according to the present invention can beproduced preferably in the following process.

Carbon fiber bundles are made by making the bundles contain powderybinder-pitch and cokes that eventually become a matrix, and, further, ifnecessary, by making the bundles contain phenol resin powder. A softcoat made from plastic such as thermo-plastic resin is made around thecarbon fiber bundle to obtain a soft intermediate material. The softintermediate material is made to have a yarn-shape (Japanese PatentApplication Laid-Open No. 2-80639), and is molded with a hot press at300 to 2000° C. at atmospheric pressure to 500 kg/cm² to obtain a moldedproduct after the necessary amount of the material is laminated.According to the demand, the molded product is carbonized at 700 to1200° C., and is made to be graphite at 1500 to 3000° C. to obtain aburned product.

The carbon fiber may be any one of the pitch-based carbon fibers thatare obtained by providing pitch for spinning use, melt-spinning thepitch, making the pitch infusible and carbonizing the pitch, and PNAbased carbon fiber that is obtained by giving flame resistance toacrylonitrile polymer (or copolymer) fiber and by carbonizing the fiber.

As an organic binder that is necessary for making a matrix,thermosetting resins such as phenol resins and epoxy resins, tar andpitch may be used, and these may contain cokes, metal, metal compounds,inorganic and organic compounds. A part of the organic binder sometimesbecomes a source of carbon.

After that, this molded product or this burned product, produced as inthe above method, and Si are held in a temperature range of 1100 to 1400under a pressure of 0.1 to 10 hPa in the furnace for at least one hour.Preferably, in the process, inert gas is allowed to flow to form aSi—SiC layer on the surface of the molded product or the burned product,in such a way that 0.1 or more than 0.1 (NL)(normal litter:corresponding to 5065 litter at 1200° C., under a pressure of 0.1 hPa)of the gas is allowed to flow per 1 kg of the total weight of the moldedproduct, or the burned product, and Si. Thereafter, the temperature israised to 1450 to 2500° C., preferably, to 1700 to 1800° C. to meltSi—SiC-based material, to impregnate the material into the inside of thepores of the above-described molded product or the burned product, andto form the material. In the process, in the case in which the moldedproduct is used, the molded product is burned to obtain thefiber-composite material.

The molded product, or the burned product, and Si are held at atemperature of 1100 to 1400° C., under a pressure of 1 to 10 hPa for onehour or more. In the process, the amount of inert gas to be used iscontrolled in such a way that per 1 kg of the total weight of the moldedproduct, or the burned product, and Si, 0.1 or more than 0.1 NL,preferably, 1 or more than 1 NL, more preferably, more than 10 NL ofinert gas is made to flow.

Thus, in the burning process (namely, in the process in which Si is notyet melted or impregnated), because providing an atmosphere of inert gasremoves the generated gas such as CO brought by the change in whichinorganic polymer or inorganic substance become ceramics from theatmosphere of burning and prevents the contamination of the burningatmosphere caused by the outside factor such as O₂ or the like in theair, it is possible to keep low porosity in the fiber-composite materialthat is obtained by melting and impregnating Si in the subsequentprocess.

In the process in which Si is melted and impregnated into the moldedproduct or the burned product, the surrounding temperature is raised to1450 to 2500° C., more preferably to 1700 to 1800° C. Then, the pressurein the burning furnace is maintained preferably in a range of 0.1 to 10hPa. The atmosphere in the furnace is preferably an inert gas or argongas atmosphere.

As described above, because the combination of the usage of the softintermediate material, the impregnation of silicon and the fusion ofsilicon brings about the retention of long and narrow pores between theyarn in the burned product or the molded product, silicon migrates intothe inner part of the molded product or the burned product along thelong and narrow pores. In the migration process, silicon reacts withcarbon in the yarn and is gradually carbonized from the surface side ofthe yarn to produce the fiber-composite material according to thepresent invention.

The inclination of concentration in Si—SiC-based material in the wholefiber-composite material layer is controlled with the porosity and thediameter of the pores of the compact or the sintered body. For example,in the case where the concentration of Si—SiC-based material layer ismade higher than any other portion at a depth of 0.01 to 10 mm from thesurface layer of the fiber-composite material, the porosity in theportion having a desired high concentration in the compact or thesintered body is made to be in the range from 5 to 50% and the averagediameter of the pores is made to be 1 μm or more. In the other portions,the porosity and the average diameter of the pores is made the same orlower than the portion having the high concentration. The porosity inthe portion having the desired high concentration of the compact orsintered body is preferably 10-50% and the average diameter of the poresis preferably 10 μm or more. It is because the binder in the compact orthe sintered body is hard to be removed if the porosity is less than 5%,and impregnation of the portion except for the portion having thedesired high concentration with the Si—SiC-based material proceedsbeyond the range of control of an amount of Si and other parameters of aproduction method such as a contact time.

In order to form the fiber-composite material layer on the surface ofC/C composite, the molded product designed to have a porosity of 0.1 to30% at least in the part near to the surface during burning ispreferably used.

In order to make the porosity in the molded product or the burnedproduct decrease from the surface toward the inside, more than onepreformed sheet, made of preformed yarn of different binder-pitch, isarranged and molded in such a way that from the inside to the surfacelayer side the binder-pitch becomes larger.

In order to make the silicon concentration in the fiber-compositematerial layer have an incline, the burned product adjusted to have theporosity in the part near the surfaces which becomes lower from thesurface to the inside, or the molded product adjusted to have theporosity at least in the part near the surface which becomes lower,during burning, from the surface to the inside are used to produce thefiber-composite material.

Characteristics and effects of a fiber composite material of the presentinvention are hereinbelow described.

(1) Since a fiber composite material of the present invention has amatrix containing a Si phase, its porosity can be controlled to belower. If all Si reacts with C to produce SiC, pores corresponding to adifference of specific gravity are generated because specific gravitiesof Si, C, and SiC are 2, 2, and 3.2, relatively. Since the compositematerial of the present invention has a low porosity, it has a smallsurface area, and a combustion probability owing to an oxygen attack islowered. Therefore, antioxidation ability of the composite material canbe maintained in comparison with a material having a high porosity.

A fiber composite material of the present invention has a porosity ofpreferably 0.5-5%, more preferably 1-3%. When the porosity exceeds 5%,its antioxidation ability cannot be maintained. Further, large pores ormany pores are present. Therefore, when the composite material is usedas a sliding material, it increases the possibility that much of theother sliding material is scraped and kept inside the pores duringsliding and that the composite material, which is a sliding material,breaks.

When the porosity is lower than 0.5%, the following phenomenon, whichhappens in a conventional SiC—C/C composite material, is prone to occurpartially.

(2) Further, in the case of a conventional Si—C/C composite material, aporosity had to be increased so as to completely leave fibers oruniformly disperse fibers and SiC wholly.

The reason is as follows: Si is reacted with C at a higher temperaturein order to completely fill the pores. Further, paths for permeating Siof a C/C substrate to be impregnated are uneven. This hinders a smoothflow of Si. Therefore, a reaction producing SiC completely proceeds inportions where the paths are clogged with Si, and fibers in the portionsare destroyed. On the other hand, the reaction producing SiC proceedsvery little in a periphery of fibers in portions where Si does notreach. Thus, the conventional composite material becomes very uneven onthe whole.

On the contrary, in the composite material of the present invention, aflow path for permeating Si into the C/C substrate is very uniformlyformed three-dimensionally. Therefore, the composite material is freefrom the problems of partially having a strong re action producing SiCor insufficiently having the reaction producing SiC. Thus, a homogeneousthree-dimensional composite material can be obtained.

(3) Further, a fiber composite material of the present invention has aself-repairability by Si which remains with an inclination of aconcentration besides SiC and C/C composite.

A material containing only SiC and C/C composite causes a strain betweenC and SiC during heating because their thermal expansion coefficientsare different from each other, thereby forming a crack. The crack isnever repaired.

On the other hand, in the case of a fiber composite material of thepresent invention, Si is present on the outer surface of SiC asdescribed above. Therefore, self-repairing can be conducted by apenetration of molten Si into the crack, or self-glazing can beconducted by generation of SiO₂ by Si oxidation. That is, the materialhas self-repairability.

(4) Further, in a fiber composite material of the present invention,which contains Si, a thermal resistance or an electric resistance isprone to be changed more greatly when the material is reduced byexcessive abrasion. Therefore, the material can exhibit a function of asensor. Additionally, when a temperature of Si rises unusually in a highvacuum, Si evaporates at about 1400° C., which is sufficiently lowerthan 2700° C., at which SiC is sublimated. Therefore, a sensing functionthat can warn of an extraordinary state by confirming a change of weightor by changing of electrical, thermal properties can be exhibited.

Hereinafter, the present invention is illustrated in more detail byexamples, however, the present invention is not limited to the examples.

The properties of the composite materials obtained by each example aremeasured by the methods as described below.

Method of Measuring Porosity

porosity (%)=[(W3−W1)/(W3-W2)]×100

By Archimedes Method

Dry weight (Wl): measured after drying the sample at 100 for 1 hour inan oven.

Under water weight (W2): measured in water after boiling the sample inwater and making water migrate into the pores completely.

Drinking weight (W3): measured at atmospheric pressure after makingwater migrate into the sample completely.

Method of Evaluating Oxidation Resistance

The oxidation resistance is measured by measuring the loss rate ofweight, after 200 hours, of the sample cut out as a test piece of 60mm×60 mm×5 mm (thickness), held for 200 hours at 1150° C. in a furnace(1%O₂, 99%N₂).

Method of Evaluating Compressive Strength

Compressive strength is calculated using the compression-loaded testpiece with the following formula.

Compressive strength=P/A

(in the formula, P is the load when loaded with the maximum load, A isthe minimum sectional area of the test piece.)

Method of Evaluating Durability Under Oxidative Condition at HighTemperature

The weight of the cut out test piece, is measured, of 60 mm×60 mm×5 mm(thickness), held at 1200° C. using a mixed gas of 99% of Ar and 1% OfO₂.

Method of Evaluating Interlaminar Shear Strength

Interlaminar shear strength is calculated with the following formula,after three-point bending, regarding the distance of the test piecethickness h multiplied by 4 as the distance between the supports.

Interlaminar shear strength=3P/4bH

In the formula, P is the maximum bending load when broken, and b is thewidth of the test piece.

Method of Evaluating Bending Modulus

Bending modulus is calculated with the following formula, using theinitial gradient P/σ of the straight part of load-deflection curve,after three-point bending, regarding the distance of the test piecethickness h multiplied by 40 as the distance between the supports.

 Bending modulus=1/4 L ³ /bh ³ p/σ

(in the formula, b is the width of the test piece)

Method of Evaluating Self-restoration

Self-restoration is measured on the test piece annealed for 2 hours at900° C., after making micro-cracking inside by applying repeatedstresses of Max: 20Mpa to Min: 5 Mpa, 100,000 times.

Method of Evaluating Dynamic Coefficient of Friction

The frictional force Fs(N) is measured on the test piece of 60 mm×60mm×5 mm (thickness) mounted on a rotary jig and pressed against thepartner material (SUJ, 10 mm ball) with a constant load Fp(N).

The dynamic coefficient of friction is calculated with the followingformula.

Coefficient of frictionμ=Fs/Fp

Method of evaluating specific abrasive wear

The weight untreated, Wa (mg) and the weight treated, Wb (mg) aremeasured on the test piece, size of which is 60 mm×60 mm×5 mm(thickness), mounted on a rotary jig and pressed against the partnermaterial (SUJ, 10 mm ball) with a constant load P. Abrasive wear V (mm³)is calculated with the following formula, using the density ρ (g/cm³) ofthe test piece.

V=(Waρ.Wb)/ρ

Specific abrasive wear Vs (mm^(3/)N.km)) is calculated with thefollowing formula, using abrasive wear V (mm³), test load P (N) andsliding distance L (km).

Vs=V/(P·L)

EXAMPLE 1

By impregnating phenol resin in carbon fibers pulled and aligned in onedirection, about ten thousand carbon long fibers of diameter 10 μm weretied in a bundle to obtain a fibrous bundle (yarn). The yarn wasarranged as shown in FIG. 1 to obtain a prepreg sheet.

Then, the prepreg sheet was laminated so as to have 50 layers andprocessed at 180° C. and at 10 kg/cm² with a hot press to cure thephenol resin and was burned at 2000° C. in nitrogen to obtain a c/ccomposite. The obtained c/c composite had a density of 1.0 g/cm³ and aporosity of 50%.

The c/c composite was then vertically placed in a carbon crucible filledwith silicon powder of purity 99.8% and of mean particle size 1 mm.After that, the crucible was moved into a furnace. The c/c composite wasprocessed to impregnate silicon into the composite and produce thefiber-composite material according to the present invention, under thefollowing condition: the furnace temperature of 1300° C., the flow rateof argon gas as inert gas of 20 NL/minute, the furnace internal pressureof 1 hPa, the holding time of 4 hours and then the furnace temperaturewas raised to 1600° C. while the same furnace pressure was kept. In thisExample, the whole c/c composite was changed to the fiber-compositematerial of the present invention.

The measured results such as density, porosity, shearing strength amonglayers, compression strength and bending modulus of the obtainedfiber-composite material are shown in Table 1.

Each of the data were measured on a test piece cut from near the surfacelayer in which Si—SiC type material and C/C composite were adequatelycombined.

FIG. 6 is a color photograph of EPMA (electron beam micro analyzer) thatshows the constitution of a ceramic material in the sectional directionto the surface layer of the test piece. FIG. 7 is a color photograph ofreflective electronic image by SEM showing the constitution of the sameceramic material. FIG. 8 is a schematic cross sectional view based onFIG. 6 and FIG. 7 showing the microstructure at the boundary areabetween the yarn.

The color photographs of FIG. 6 and FIG. 7 show that Si and C have amicro-and fixed concentration gradient of about 0.01 to 0.1 mm scale.That is, as shown in FIG. 8, silicon-carbide phase 5C has grown alongthe surface of yarn 2B on the side near the surface of yarn 2B amongmatrix 8B and silicon phase 4C has grown inside the phase 5C. It isbecause the constitutional difference between the phases 4C and 5C canbe observed from FIG. 7 and, as in FIG. 6, both of carbon and siliconexist in the phase 5C, but carbon is not observed in phase 4C.

EXAMPLE 2

The C/C composite produced in the same way as Example 1 was impregnatedwith phenol resin and was burned at 2000° C. in nitrogen after the resinwas cured at 180° C. in an oven under normal pressure. By repeating theprocess further five times, a C/C composite was obtained. The obtainedC/C composite had a density of 1.4 g/cm³ and a porosity of 30%.

After that, the obtained C/C composite was impregnated with Si in thesame way as Example 1 to produce a fiber-composite material.

The measured results such as density, porosity, shearing strength amonglayers, compression strength and bending modulus of the obtainedfiber-composite material are shown in Table 1. Each of the data weremeasured on a test piece cut from near the surface layer of thefiber-composite material in which Si—SiC type material and C/C compositewere adequately combined.

EXAMPLE 3

A fiber-composite material comprising fiber-composite-material layerswas produced.

A C/C composite was produced by the following process.

Preformed yarn was produced by the preformed yarn method (JapanesePatent Application Laid-Open No. 2-80639). One-direction-preformed-yarnsheets were produced using the preformed yarn. The sheets were laminatedin such a way that the carbon fibers were intersected at right angleswith each other, and were molded at 600° C. and at 100 kg/cm² with a hotpress. The obtained C/C composite had density of 1.8 g/cm³ and porosityof 10%.

The obtained C/C composite was impregnated with Si in the same way asExample 1 to produce a fiber-composite material. The fiber-compositematerial layer had a thickness of 10 mm.

The measured results such as density, porosity, shearing strength amonglayers, compression strength and bending modulus of the obtainedfiber-composite material are shown in Table 1. Each of the data weremeasured on a test piece cut from near the surface layer of thefiber-composite material in which Si—SiC type material and C/C compositewere adequately combined.

EXAMPLE 4

A fiber-composite material comprising fiber-composite-material layerswas produced in the same way as Example 1. However, boron nitride wasadded in the process of producing the C/C composite so that boronnitride is contained in the fiber-composite-material layers. Thefiber-composite-material layer was designed to have a thickness of 30mm.

The measured results such as density, porosity, shearing strength amonglayers, compression strength and bending modulus of the obtainedfiber-composite material are shown in Table 1. Each of the data weremeasured on a test piece cut from near the surface layer of thefiber-composite-material in which Si—SiC type material and C/C compositewere adequately combined.

EXAMPLE 5

A fiber-composite material comprising fiber-composite-material layerswere produced in the same way as Example 1. In this Example 5, Siconcentration in fiber-composite-material layer was designed to have agradient in such a way that the concentration becomes low from thesurface to the inside. The fiber-composite-material layer was planned tohave a thickness of 3 mm. The concentration gradient of Si was designedto incline in a range of 100/0 to 0/100 compared with the amount ofcarbon fiber from the surface to the inside of thefiber-composite-material layer.

A C/C composite was produced by the following method.

Ten types of preformed yarn were produced at the rate of the binderpitch in the preformed yarn of 20 to 60 by the preformed-yarn method.One-direction preformed sheets were produced using this preformed yarn.The preformed sheet having the binder pitch rate of 20 was placed in thecenter of the thickness, the preformed sheet was placed in order in sucha manner that the binder rate becomes high toward the surface layer, andthe preformed sheet having the binder pitch rate of 60 was placed in thenearest side to the surface. Then, these preformed sheets were laminatedin such a way that the carbon fibers were intersected at right angleswith each other, and were molded at 600° C. and at 100 kg/cm² with a hotpress. After that, these preformed sheets were burned at 2000° C. innitrogen to obtain a C/C composite. The obtained C/C composite haddensity of 1.6 g/cm³ and porosity of 10%.

The obtained C/C composite was impregnated with Si in the same way asExample 1 to produce a fiber-composite material.

The measured results such as density, porosity, shearing strength amonglayers, compression strength and bending modulus of the obtainedfiber-composite material are shown in Table 1. Each of the data weremeasured on a test piece cut from near the surface layer of thefiber-composite material in which Si—SiC type material and C/C compositewere adequately combined.

Comparative Example 1

A C/C composite was produced in the same way as Example 3.

The measured results such as density, porosity, shearing strength amonglayers, compression strength and bending modulus of the obtainedfiber-composite material are shown in Table 1.

TABLE 1 Density Porosity Interlaminar Specific Dynamic of body of bodyCompressive Bending shear abrasive coefficient Oxidation materialmaterial Density Porosity strength modulus strength wear (mm³/ offriction Self- resistance (g/cm³) (%) (g/cm³) (%) (Mpa) (Gpa) (Mpa) (N ·km) (μ) restoration (%) Example 1 1.0 50 2.2 1 to 2 190 40 22 0.0 0.55140/190 4 2 1.4 30 2.1 1 to 2 180 45 20 0.0 0.18 120/180 6 3 1.8 10 2.01 170 48 18 0.0 0.05 100/170 10  4 1.4 50 2.1 1 to 2 200 55 23 0.0 0.26115/200 6 5 1.6 50 to 10 2.1 1 to 2 190 45 20 0.0 0.21 130/190 4Comparative 1 1.8 10 — — 140 50 16 0.55 0.05 0 (none)/150 100  Example

Table 1 suggests that the fiber-composite materials (Examples 1 to 5)according to the present invention show good results in compressionstrength and in shearing strength compared with C/C composite(Comparative Example 1), and that the fiber-composite materials showalmost the same result in bending modulus compared with C/C composite.In the fiber-composite materials according to the present invention,impregnating Si—SiC type material into C/C composite makes the C/Ccomposite stronger in compression strength than C/C composite alone. Itis thought that it is because the Si—SiC type material forms amongcarbon fibers.

The fiber-composite material including boron nitride (Example 4) showeda better result in bending modulus than other examples. Moreover, thefiber-composite material with the gradient of Si concentration infiber-composite material layers (Example 5) showed a better result inself-restoration than other Examples.

Industrial Applicability

As described above, because the fiber-composite material according tothe present invention has a configuration in which the fundamentalstructure is composed of body material made of C/C composite and thebody material is impregnated with Si—SiC, the fiber-composite materialhas high-impact properties, lightweight properties and high strengthproperties, which are characteristics of C/C composites, and highoxidation resistance, high creep resistance and spalling resistance,which are not characteristic of C/C composites.

Further, in the fiber-composite material according to the presentinvention, making Si concentration in the fiber-composite material layerhave an inclination in such a way that the concentration becomes lowfrom the surface to the inside can remarkably improve corrosionresistance and strength in oxidation and corrosion environments, andhealing function to the defects in the surface and subsurface parts.

In the fiber-composite material according to the present invention,making the fiber-composite material layer comprise boron nitride canprevent toughness deterioration of c/c composite portion by beingimpregnated with Si—SiC-based material.

What is claimed is:
 1. A fiber-composite material comprising: aplurality of first yarns arranged in a first layer, each first yarnextending in a first longitudinal direction, and comprising a bundle ofcarbon fibers and an additional carbon component; a plurality of secondyarns arranged in a second layer, each second layer extending in asecond longitudinal direction and comprising a bundle of carbon fibersand an additional carbon component, said second longitudinal directionbeing substantially perpendicular to said first longitudinal direction;and a Si—SiC matrix for three-dimensional integrating the yarns to oneanother, said matrix being interposed between adjacent yarns within eachlayer and between yarns of adjacent layers; wherein said fiber-compositematerial is formed by a method comprising the steps of: forming aplastic coating around each of said first and second yarns; stacking theplurality of first and second yarns on one another along said first andsecond longitudinal directions, respectively, to form an intermediateproduct; heating the intermediate product to burn the plastic coatingsand form a burned product; and infiltrating molten silicon into thepores of the burned product to form said fiber-composite material. 2.The fiber-composite material of claim 1, wherein said matrix has asilicon carbide phase grown along the surface of each yarn.
 3. Thefiber-composite material of claim 2, wherein said matrix has a siliconphase comprising silicon, and said silicon carbide phase is grownbetween said silicon phase and each yarn.
 4. The fiber-compositematerial of claim 1, wherein said matrix has an inclined composition inwhich the amount of silicon increases with increasing distance from thesurface of each yarn.
 5. The fiber-composite material of claim 1,wherein said matrix defines a three-dimensional network structurethroughout said material.
 6. A method of preparing fiber-compositematerial, comprising the steps of: producing bundles of carbon fiber byimpregnating a component of powdery carbon into the bundles of carbonfiber, which eventually forms a matrix shape; forming a plastic coataround the bundles of carbon fiber to obtain an intermediate material;molding the intermediate material to obtain a molded product by makingthe intermediate material into a yarn-shape and laminating apredetermined amount of the material, or burning the molded product toobtain a burned product; holding the molded product or the burnedproduct and Si, at 1100 to 1400° C. in an atmosphere of inert gas; andheating the molded product or the burned product and Si to a temperaturefrom 1450 to 2500° C., to thereby impregnate Si—SiC-based material intothe inside of pores of the molded product or the burned product.
 7. Amethod of preparing fiber-composite material as claimed in claim 6,wherein the molded product or the burned product and Si are held at atemperature of from 1100 to 1400° C. under a pressure of 0.1 to 10 hPafor one or more hours, and an inert gas is controlled to flow in anamount of 0.1 or more normal litters (NL) per 1 kg the total weight ofthe molded product or the burned product and Si.
 8. A method ofpreparing fiber-composite material as claimed in claim 6, wherein themolded product or the burned product and Si are heated to a temperatureof from 1450 to 2500° C. under a pressure of 0.1 to 10 hPa.
 9. A methodof preparing fiber-composite material as claimed in claim 7, wherein themolded product or the burned product and Si are heated to a temperatureof from 1450 to 2500° C. under a pressure of 0.1 to 10 hPa.